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Can I Install Tile Over My 24" o.c. Floor?
QUESTION
Can I install tile over my 24" o.c. floor? - I did have a general question about a tile job I am considering for my sunroom. It measures 12 by 24 and the space below is finished so I can’t access the joist. The situation I am running into is the space between the joist. This house was built 7 years ago and since I selected a vinyl floor, the builder placed my joist 24 inches on center. The builder has recommended hardwood over tile for the job but thought a 3/8 or ½ inch piece of plywood with Ditra on top would also suffice.My local tile shop is pushing hardy backer. (Room is climate controlled and fully finished) My question- Is tile even a good idea for this situation and if so, what would you recommend. I am looking at a standard 12 by 12 ceramic tile.
ANSWER
ANSWER - It is definitely a good idea. If you have a sun room then you want to have cementitious material under the tile in order to take advantage of the energy savings from the passive solar benefits of tile and concrete substrates. I'm not a big fan of ditra, but in some cases it might work. I do believe they do allow for 24" o.c. spacing. 1/2" hard backer board might work, but you will have to check their data sheets. I think they only allow 19.2" spacing.There are 24" o.c. joist methods that are recommended. You can apply a 3/8" exterior-glue laminated birch wood panel with a minimum of 7 piles over a 23/32" t & g exterior-glue plywood per TCNA F160 and bond directly to it. The key is not to have excessive deflection which would be more than L/360. You have a relatively small area so depending on how the floor was constructed and braced it might meet that. You need to make sure you have movement joints along the perimeter of the room to allow for movement within the tile assembly. Those joints can be left open and covered by a base board or tile, or you can fill them with a silicone or urethane sealant that meets ASTM C920. good luck.
2 thoughts on “Can I Install Tile Over My 24″ o.c. Floor?”
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24″ OC joist. OK . But what size joists ? I presume TJI -type ? What series & depth ? What kind of subfloor ? 3/4 ply ? 1.125 Advantech ? The floor is a system.
The total deflection under what conditions matters most. Put a cup of water mid floor and walk / jump around. The motion of the water will give you an idea of the floors stiffness. If it splashes out !:o , there are some nice waterproof tiles these days 😉 Hang a plumb bob just touching the floor or even a really tight string across the room and load it up. Measure the sag in the floor.
As you point out there are many variables to what contributes to what the actual deflection is within the floor. There is no practical method for testing the floor for deflection in situ. You need an engineer to actually perform the mathematical calculations based the various dimensions and physical properties of the floor components. The rule of thumb for the layman is performing qualitative testing by using the full glass of water on the floor and jumping up and down to detect excessive movement. For walls you can just push on the wall and if you feel it move, then it is too much deflection. The only way to provide a valid measurement is by having an engineer do the math.
The Tile Council of North America Handbook for Ceramic, Glass, and Tile Installations (TCNA) does provide details for different raised wood flooring configurations. They have details for 16″o.c., 19.2″ o.c., and 24″ o.c.. TCNA F155-25 Joist max. 24″ o.c./Plywood or OSB Subfloor for Ceramic Tile. It is based on tile assemblies not being more than 7 lbs/sf. It must be compliant with current International Residental Code (IRC). I-joists with minimum 1.5″ Top Flange with cross bracing. 23/32″ T&G OSB or Plywood with 1/8″ gap between sheets with sheets staggered to each other. With minimum 19/32″ exterior glued plywood. With sheets staggered to subfloor and adjacent sheets. Of course with proper nailing of the sheets.